In a current optical core network, an optical transmission standard called “Optical Transport Network (OTN)” is widely used as a base platform. In OTN, data is transmitted using Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH), which is a standard for a digital synchronous transmission method used for an existing telephone service and the like.
A transmission apparatus having a transmission method in which SONET or SDH is used, transmits a synchronous multiplexed signal that an overhead signal (OH) is added to a multiplexed data signal. The OH is a signal for performing monitoring, maintenance, and operation of the transmission apparatus and a communication network. The synchronous multiplexed signal may be referred to as a “frame” as a unit thereof hereinafter. By adding overhead data to a frame, the reliability of data transmission can be improved.
By having appropriate information in a processing module that provides overhead function, it is possible to realize monitoring, maintenance, and operation according to demands in the operation management of data transmission. For example, a signal fail (SF) and signal degradation (SD) on a receiver of the transmission apparatus are detected as failure. By adding Automatic Protection System (APS) bytes (K1 and K2 bytes) in which such information (SF and SD) has been had to a frame, another transmission apparatus is notified of information regarding the transmission apparatus in order to perform switching control. In addition, by adding JO byte having a section tracing function to a frame, it is possible to monitor connection of paths. Since the usage of overhead is different between users, it is necessary to change a specification of the overhead function different in each user. The “overhead function” herein refers to a function realized by transferring overhead, and the “specification change of the overhead function” herein refers to, for example, a specification change of data included in overhead.
Technologies used for a specification change of the overhead function as described below have been proposed. One of the technologies is a technology in which a specification of the overhead function is changed by upgrading firmware so as to change a setting value of a processing module that performs setting of a data signal. In addition, another technology has been proposed in which a processing module that provides the overhead function is configured by a Field-Programmable Gate Array (FPGA) that can be overwritten. In this technology, when a specification change of the overhead function needs to be performed, the FPGA is overwritten, and then reconfiguration is performed to change the specification of a processing module that provides the overhead function. Furthermore, another technology has been proposed in which an FPGA that configures the processing module that provides the overhead function is duplicated. In this case, when one of the FPGAs is subjected to a specification change, the other FPGA is selected and used to perform processing, and then the FPGA that has been subjected to the specification change is selected and used to perform processing (For example, refer to Japanese Laid-open Patent Publication No. 2005-80037).